Nowadays, for the drilling equipment at home and abroad, the most ideal, the most popular, and matured coring method is the wire-line coring, i.e., using the steel wire rope. In 1947, the American Boart Longyear Company invented the technology of wire-line core drilling, which became a series of products till 1950s. In 1972, Ministry of Geology and Mineral Resources of P. R. China started researching the technology of wire-line core drilling. In the early 1980s, this technology was widespread and used domestically. Up to now, the drilling range of the wire-line coring is always used in a vertically downward angle. Since the internal pipe of the core needs to rely on its gravity to droop to the bottom of the hole, the limitation of the drilling angle cannot be exceeded. Meanwhile, the horizontal drilling and the downhole drilling have shallow hole locations and many angles. For example, for the downhole drilling, the space is narrow, and the roadway of 2×2 meters is mostly used. The wire-line coring and the tower supporting the wire-line cannot be used. Even if the technology of wire-line coring is applied, the space of the downhole needs to be enlarged, which costs time, labor, and money. Therefore, this process is generally not used.
A double-pipe coring process is used in another core drilling method. This technology was introduced from abroad in the 1950s. In order to extract the core, all drill rods need to be pulled out. After the core is retrieved, the drill rods are linked and put back into the hole. Taking out and putting back drill rods is labor intensive and time-consuming. Also, taking out drill rods will leave the hole unsupported by the drill rods, causing drilling accidents, such as collapsing, piece-dropping etc. inside the hole. When the core internal pipe is fed in, the collapsed and dropped pieces of rock may be loaded, leading to a mess of the core, self-grinding of the core, and a low sampling ratio which cannot meet the national standard. In the late 1980s, the technology of double-pipe coring is generally not used in the earth surface drilling. At present, the technology is usually used in multi-angle drilling industries, such as horizontal drilling, downhole drilling, and so on.
The pre-stressed steel strand was the construction material invented by a Frenchman, Enugene Freyssinet, in 1928. China started producing this material in the 1960s. The pre-stressed steel strand is broadly used in construction, railroad, highway, hydraulic engineering, energy, and rock anchoring construction. The pre-stressed steel strand can stand bending without cracking, expanding, and flaking off. It has nice impact property, good toughness, and can be wound circularly, and occupies a small area. When the pre-stressed steel strand is used in the technology of core drilling, cumbersome wire-line tower and high-duty pump are not required. Moreover, the downhole space does not need to be enlarged to increase the working efficiency. Therefore, it is more convenient and efficient in terms of transportation and on-site usage.